1. Field of Invention
This invention relates to tunable optical wavelength converters for communications using optical fibers.
2. Technical Background
Wavelength Division Multiplexing (WDM) increases communication capacity of optical fibers. WDM uses different wavelengths of light to transmit independent information so that multiple communication channels can be provided using a single fiber. Thus, WDM systems provide upgrades of communication capacity without costs of additional fibers.
To implement WDM, wavelength converters are used to convert existing optical signal transmitters to change a source wavelength into a target wavelength so that wavelengths can be allocated to independent sources. Current wavelength converters based on an interferometer depend on critical phase adjustments of the interferometer to completely cancel the output laser signal. If the output signal is not completely canceled, remaining output signal continues to be transmitted and thus reduces the signal-to-noise ratio of the optical system. Complete cancellation requires exactly 180 degree phase shifts. Thus, precise phase shifts are required for optimal system performance. However, exact phase shifts are difficult to achieve. Thus, there is a need for a wavelength converter that achieves high signal-to-noise ratio without stringent phase shift requirements.